A conventional navigation apparatus displays the current position of a vehicle which is determined by a vehicle position determining unit on a digital map (simply referred to as a “map” from here on) displayed on a display unit while superimposing the current position on the map. Furthermore, the conventional navigation apparatus searches for a recommended route from the current position of the vehicle which is determined by the vehicle position determining unit to a destination inputted via an input unit, and displays the recommended route on the map. The conventional navigation apparatus then carries out a route guidance of the recommended route on the basis of the shapes of road links read from a recording medium.
By the way, recent years have seen increase in the number of cars owned by individuals and occurrence of traffic congestions in various places of roads. Especially, most of vehicles travelling along a highway or expressway (simply referred to as a “highway” from here on in this specification) which is extending toward a big city and which is used for commuting or the like are occupied by only one person and this results in increase in traffic congestions. In order to solve this problem, there have been constructed highways where traffic is restricted by law according to the conditions of vehicles including the number of passengers and vehicle types.
For example, a car pool lane (Car Pool Lane) which is adopted by a road system mainly seen in big cities of North American is an example. A car pool lane is also called an HOV lane (High Occupancy Vehicle Lane) , and is a lane along which, for example, only vehicles in each of which two or more persons are riding are granted to travel. For example, a lane which is also provided on a highway is known as a car pool lane. A road system which adopts such a car pool lane provides users with a preferential treatment that makes it possible to arrive at the destination in a shorter time when they travel along a car pool lane so as to prod users to share a vehicle with one or more persons, thereby reducing the traffic as a whole and therefore reducing traffic congestions.
As a technology relevant to such a car pool lane, patent reference 1 discloses a vehicle-mounted navigation apparatus which searches for a recommended route in consideration of the number of passengers. This vehicle-mounted navigation apparatus has a storage unit for storing map data including link data about each link which constructs a road on a map. As for a car pool link on which restrictions of prohibiting a vehicle which is not occupied by two or more persons from traveling are imposed, the vehicle-mounted navigation apparatus uses link data including information showing that such restrictions are imposed on the car pool link to search for a recommended route from the place of departure to the destination. Furthermore, when a car pool link is included in the constitution links which construct the recommended route, the vehicle-mounted navigation apparatus receives an input of the number of passengers, and searches for a recommended route from the place of departure to the destination by using the link data to exclude links along which the vehicle cannot travel because the received number of passengers does not meet a certain criterion.
Patent reference 2 discloses a route searching apparatus which can perform a search for a route in consideration of the conditions of a vehicle through an easy operation. This route searching apparatus is provided with a map data acquiring unit for acquiring map data defined by nodes and road links, a route searching unit for searching for a route to a destination before the conditions of the vehicle are set up, taking into consideration a road link corresponding to a particular road for which whether or not the vehicle can travel according to the conditions of the vehicle is determined, the road link being included in the map data acquired by the map data acquiring unit, and an output unit for outputting the route searched for by the route searching unit.    [Patent reference 1] JP,2005-061988,A    [Patent reference 2] JP,2005-083758,A
In many cases, a car pool lane currently provided is disposed as a central one of a plurality of lanes of a highway. A problem is therefore that when a vehicle enters a highway from a local street via an entrance of the highway or a connection road to the highway and then enters a car pool lane from an general purpose lane of the highway, the vehicle has to cross a plurality of driving lanes of the highway along which many vehicles are travelling at a high speed until entering the car pool lane, and this entails danger to the driver of the vehicle and forces the driver to do a burdensome driving operation. Furthermore, because the number of vehicles which are travelling along a highway at a high speed changes greatly depending on what day of the week it is or what time zone it is, and low-acceleration vehicles and large-sized vehicles also travel along a highway, it is dangerous to cross a plurality of driving lanes. This problem similarly arises in a case in which a vehicle goes out of a car pool lane to a highway via an exit of the car pool lane, crosses a general purpose lane of the highway, and then goes out of the highway to a local street via an exit or a connection road of the highway.
However, no measures against the above-mentioned problem are taken in the route search of conventional navigation apparatuses, and conventional navigation apparatuses simply perform a search for a route including a car pool lane as a part thereof. Therefore, even if a section in which the vehicle uses a car pool lane is short, a recommended route including the car pool lane is presented to the user. When the user is going to drive the vehicle along the presented recommended route, in order to enter a car pool lane from a local street via general purpose lanes of a highway, and then go out of the car pool lane to a local street via general purpose lanes of the highway, the vehicle has to drive the vehicle to cross a plurality of driving lanes of the highway two times during travel over a short distance. Therefore, the above-mentioned problem of entailing danger to the user and also forcing the user to do a burdensome driving operation is left behind.
The present invention is made in order to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a navigation apparatus which can provide a recommended route which enables the user to use a car pool lane properly and travel along the car pool lane safely for the user.